1. Field of the Invention
The present invention relates to a hybrid integrated circuit substrate, and more specifically, it relates to a hybrid integrated circuit substrate to which a magnetic circuit for a motor or the like is assembled.
2. Description of the Prior Art
FIG. 1 is a perspective view showing an example of a conventional integrated circuit substrate, which is disclosed in Japanese patent publication Gazette No. 13234/1971, for example.
Description is now made on the structure of the conventional integrated circuit substrate as shown in FIG. 1.
Referring to FIG. 1, a thin layer 22 of aluminum oxide is formed through anodic oxidation on at least one major surface of an aluminum substrate 21. On the thin aluminum oxide layer 22, conductive paths or conductor fixing portions 27 and circuit elements such as resistors 23 and 24 are formed by selectively depositing resistor materials and good conductive materials. A good thermoelectric member is deposited on the thin aluminum oxide layer 22 to form a lead portion 26, and a transistor pellet 25 is adhered to the same. External conductors (not shown) are connected to the conductor fixing portions 27.
While a hybrid integrated circuit substrate assembled with a magnetic circuit for a motor has been put into practice, the integrated circuit substrate as shown in FIG. 1 including an aluminum substrate cannot be applied to such a hybrid integrated circuit substrate for a motor since the aluminum substrate allows no passage of magnetic lines of force.
There has been proposed a hybrid integrated circuit substrate for a motor in which the aforementioned aluminum substrate is replaced by an iron substrate which passes magnetic lines of force.
FIG. 2 is a sectional view schematically showing an example of such a hybrid integrated circuit substrate employing an iron substrate.
Referring to FIG. 2, a resin layer 29 of epoxy resin or the like is adhered on the surface of an iron substrate 28, and a copper foil layer 30 is adhered to the resin layer 29. The copper foil layer 30 is etched to form conductive patterns for fixing electronic components or the like, thereby to form a hybrid integrated circuit substrate for a motor.
For example, Japanese patent Laying-Open Gazette No. 46304/1979 discloses a motor employing a hybrid integrated circuit substrate based on such an iron substrate. In such a motor, an insulating base material is adhered on the iron substrate serving as a magnetic path material through an adhesive agent, and an interconnection pattern layer is formed on the insulating base material.
In the hybrid integrated circuit substrate based on the iron substrate as shown in FIG. 2, however, the thermal expansion coefficients of iron, epoxy resin and copper are 11.times.10.sup.-6 /.degree. C., 60.times.10.sup.-6 /.degree. C. and 18.times.10.sup.-6 /.degree. C. respectively, which values are extremely different from each other. Particularly the thermal expansion coefficient of epoxy resin is extremely large, whereby the substrate is warped toward the copper side in manufacturing of the hybrid integrated circuit substrate. As the result, it is extremely difficult to form patterns on the substrate.
Further, warping takes place in a thermo cycle, to cause a problem in reliability of fittings.
In addition, the distance between coils and a rotor is changed by the warping of the substrate to exert a bad influence on rotation of the motor, leading to irregular rotation.
In the conventional hybrid integrated circuit substrate for a motor such as that disclosed in the aforementioned Japanese patent Laying-Open Gazette No. 46304/1979, further, the insulating base material for supporting the circuit elements or the like is formed independently of the iron substrate to be then adhered to the iron substrate by an adhesive agent or the like. Thus, the insulating base material itself must have considerable mechanical strength, i.e., considerable thickness in order to support the circuit elements or the like on the insulating base material, whereby a space between the iron substrate and a magnetic circuit is increased.